1. Field of the Invention
The present invention relates to a slurry for conducting a chemical mechanical polishing (CMP) process on a semiconductor material, and a preparation method thereof
2. Background of the Related Art
Generally, products of Cabot Corp. and Rodel Corp. are widely used as a conventional slurry for performing a CMP process for a semiconductor device. Those slurries are fabricated by preparing oxide fumed silica, which is an oxide, and dispersing the oxide in a solvent by hydrating the surface of the oxide with a dispersant.
A flame oxidation process, which is one of the conventional slurry preparation methods, will be described with reference to FIGS. 1A and 1B. As shown in FIG. 1A, the flame oxidation is performed by introducing a silicon halide gas into a furnace 1 in an oxygen-hydrogen atmosphere. Silica (SiO2) particles are produced, according to the following formula, at a temperature over about 1200xc2x0 C. The SiO2 particles are deposited on a bottom of the furnace 1, and the other reaction product, HCl gas, is externally exhausted. The reaction formula is SiCl4(gas)+2H2(gas)+O2(gas)SiO2(solid)+4HCl(gas).
The silica particles that result from the reaction are taken out of the furnace 1 and put into a solvent 2, such as distilled water or alcohol, as shown in FIG. 1B. Then, the slurry for the CMP process is formed by stirring the solvent 2 with a dispersant 3, such as NH4OH or KOH, and an additive 4 to increase viscosity.
The dispersant 3 dissociates in the solvent 2 and induces an electric charge on surfaces of the silica particles. The electric charges on the surfaces of the particles cause the particles to repel each other, and the silica particles are thus stably dispersed in the solvent.
The size of the slurry particles which are prepared by the flame oxidation process irregularly range from 30 nm to a few hundred nm, and many large particles are produced. The large particles easily precipitate out of the slurry, due to the force of gravity. For this reason, it is impossible to use the slurry for a long time. Also, the slurry should be continually stirred while in use to reduce precipitation of the larger particles.
In addition, when large particles are formed, the surface area of the particles for a given volume of the slurry is relatively small. As a result, the electric charge volume of the particles decreases, and the repulsion force between particles is reduced. This also shortens the life of the slurry.
Further, because the silica particles prepared by the flame oxidation method are crashed when being stirred, the shapes of the particles become angulated. The edges of such silica particles, which have high hardness, may scratch a surface of a wafer during a CMP process.
Morever, because the slurry can be prepared by dispersing the particles in the solvent 2 after formation of silica particles, the preparation process of the slurry becomes complicated.
The present invention is directed to a slurry for use in a CMP process, and to a preparation method thereof, which obviates the problems and disadvantages of the conventional art.
An object of the present invention is to provide a slurry that has a relatively long life.
Another object of the invention is to provide a preparation method for a slurry that results in a slurry having a large number of small particles, so that the particles are less likely to precipitate out of the solution.
Another object of the present invention is to provide a slurry which includes hydrate particles, which have a lower hardness than the oxide particles of a conventional slurry, to thereby prevent scratching of a semiconductor wafer surface.
A slurry embodying the present invention includes a solvent, and hydrate particles dispersed within the solvent. The hydrate particles may comprise of aluminum hydrate or silicon hydrate. Preferably, the particles are substantially spherical and have a diameter of less than approximately 50 nm.
A method embodying the present invention include the steps of putting an organic matter into a solvent; adding a dispersant to the solvent to form a solution; hydrolyzing the solution; stirring the solution; and heating the solution. The organic matter added to the solvent may comprise aluminum or silicon. The dispersant added to the solvent may comprise nitric acid. The heating step may comprise heating the solution in a reaction vessel that includes a condenser, so that substantially all the solution that evaporates during the heating process is condensed and returned to the solution.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.